1. Field of the Invention
This invention relates to defoaming agents for petroleum products (such as diesel fuel and lubricating oils) and crude oil demulsifying agents, and methods for using them.
2. Description of Related Art
Diesel fuel is a mixture of a variety of hydrocarbons. Most of the hydrocarbons are aliphatic, but aromatics may be present at up to twenty to twenty-five weight percent of the fuel. The mixture can also include kerosine or gas oil. Diesel fuel is commonly used in motor vehicles, and has a tendency to foam profusely when it is poured into the fuel tank of a motor vehicle. It is therefore desirable to reduce such foaming, which can be accomplished by the addition of a defoamer.
Oil companies treat diesel fuel with organic additives, such as detergents, cetane improvers, viscosity breakers and occasionally perfumes (collectively referred to as "DAP"). Each oil company has its own preferred DAP which it typically uses only for mixing with its own fuel. All of these organic additives must be compatible with the defoamer.
Diesel fuels delivered to filling stations also may contain some amount of dispersed or dissolved water which can adversely affect the performance characteristics of previously known defoamers. The water causes a decay in defoaming characteristics and in some extreme cases, may cause the defoamer to enhance foaming, rather than suppress it. Such wet defoamers also can result in increased sludge deposition in the fuel tank.
U.S. Pat. No. 4,690,688 issued to Adams et al. discloses a typical prior art polysiloxane for use as a defoamer, wherein the polysiloxane is a copolymer with polyether side chains that provide at least 25 weight percent of the copolymer. However, these polysiloxane copolymers do not work well in wet diesel fuel because the ethers, as a hydrophilic material, will tend to stabilize the foaming of wet fuel. Additionally, to function properly these polysiloxanes must be present at levels in diesel fuel above those desirable in engine systems.
DE 4032006 describes a process for defoaming and/or degassing organic systems, including diesel oil, by adding a foam suppressant containing an organo-polysiloxane with unsaturated sidechains. A disadvantage of this foam suppressant is that it contains high levels of silicon, which can be harmful to engines. In addition, it can be incompatible with DAP and does not age well.
Lubricating oils are often comprised of mixtures of a hydrocarbon base (for example, mineral oil) and components which enhance lubrication performance (esters, for example). For instance, typical oils contain highly refined parafinic hydrocarbon stock, or synthetic polyolefins. During application and use (for instance, in lubricating gear boxes or turbines), such lubrication oil products have a tendency to foam abundantly. Such foaming, in combination with the propensity in moving machinery parts for air to be trapped, can adversely affect the lubricity, which can be detrimental to fast moving parts of machinery. Consequently, abatement of foam and rapid deaeration of lubricating oils is a serious technical requirement for use of lubricating oils.
Standard silicone oils can be used to prevent foaming of lubricating oils, and are efficient defoamers at very low rates (about 10-20 ppm). However, their use usually results in an undesirably low deaeration rate. The more efficient the silicone oil defoamer is the more pronounced is the problem of deaeration. For instance, silicone oils typically trap and retain air for about 10 minutes after the stream of passing air is switched off.
Organic defoamers (such as polyacrylate-based defoamers, which are presently popular in the art) are effective lubrication oil defoamers at concentrations from about 100-200 ppm. However, their efficiency as defoamers is very low at concentrations between about 10-50 ppm. While organic defoamers provide a satisfactory deaeration rates, the treat rates are undesirably high, and are even several times higher than the treat rates for silicone oils.
In testing these current defoamers, a strong stream of air is passed through oil during predetermined time and measuring the density of such frothed oil with time. The density of froth formed is much lower than that of a virgin air-free oil. The faster dearation means that the density of oil will be higher after, for example, 10 minutes. Thus, for an oil having a density of 0.872 the initial froth density is 0.810 due to air whipped; it regains its original value for untreated oil after 10 minutes while the densities after 10 minutes are 0.832 and 0.844 for oil treated with 10 ppm of silicone oil or 200 ppm of organic defoamer, respectively.
In general, in the petroleum industry, before oil is shipped from a refinery it must go through a process of demulsification, whereby undesired water is separated from the crude oil and removed. Currently, demulsification is carried out using an organic demulsifier, such as TROS6002X produced by TROS Company, in amounts of about 100 ppm. The organic demulsifier is usually dissolved in an aromatic compound, and then added to crude oil to effect demulsification. The amount of demulsifier depends on the type of crude oil and amount of water in the crude oil.